Polypeptide hormones can have very selective behavioral effects; however, the functional organization of the neuronal targets of these hormones and the cellular mechanisms by which they cause their effects are mostly unknown. To study these questions we propose to investigate the effects and sites of action of the polypeptide egg-laying hormone (ELH) of Pleurobranchaea. Pleurobranchaea has been chosen for this study because its nervous system is accessible to neuronal circuit analysis and because ELH-containing extracts cause egg laying and a selective suppression of feeding behavior. Our preliminary data shows that a feeding suppressing factor co-purifies with ELH on Sephadex G-50 and that ELH-containing extracts suppress correlates of feeding in the isolated nervous system. Our working hypothesis is that feeding behavior is suppressed by a direct effect of ELH on the circuitry controlling feeding. We intend to examine this hypothesis by the following procedures: (1) purify ELH, (2) test whether the feeding suppressive effect co-purifies with ELH, (3) locate binding sites of radioactively labeled ELH on identifiable neurons using autoradiographic techniques, and (4) in collaboration with William J. Davis, analyze electrophysiological effects of purified ELH on the circuitry controlling feeding. We expect to identify targets of ELH by the above procedures and to determine whether they are widespread throughout the nervous system or are localized to a few strategically located cells. This research should demonstrate whether hormone targets have special functional roles in the behavior they affect and should lay the groundwork for future cellular studies on biophysical and biochemical mechanisms. These results would thereby increase our understanding of polypeptide hormone action on the nervous system and possibly have impact on understanding hormone-caused dysfunctions.